This invention relates to waterborne coating compositions, especially thermoset waterborne coating compositions intended for use in the automotive and/or transportation industries.
Curable coating compositions such as thermoset coatings are widely used in the coatings art. They are often used as topcoats in the automotive and industrial coatings industry. Color-plus-clear composite coatings are particularly useful as topcoats where exceptional gloss, depth of color, distinctness of image, or special metallic effects are desired. The automotive industry has made extensive use of these coatings for automotive body panels.
The effect of the coating process on the environment and the effect of the environment on coatings have increasingly shaped the coatings art in the last few decades. The industry has put considerable effort into developing coatings with materials that will be less harmful toward the environment. One area of interest relates to waterborne coatings. Such coatings generally contain lower levels of volatile organic compounds.
However, it has been difficult to devise coatings, especially waterborne coatings, which will also have the desired resistance to environmental degradation in conjunction with other acceptable film performance properties.
For example, color-plus-clear composite coatings require an extremely high degree of clarity in the clearcoat to achieve the desired visual effect. High-gloss coatings also require a low degree of visual aberrations at the surface of the coating in order to achieve a high distinctness of image (DOI). As such, these coatings, whether solvent borne or waterborne, are especially susceptible to a phenomenon known as environmental etch. Environmental etch manifests itself as spots or marks on or in the finish of the coating that often cannot be rubbed out.
It is often difficult to predict the degree of resistance to environmental etch that a high gloss or color-plus-clear composite coating will exhibit. Many coating compositions known for their durability and/or weatherability when used in exterior paints do not provide the desired level of resistance to environmental etch when used in high gloss coatings such as the clearcoat of a color-plus-clear composite coating. Many compositions have been proposed for use as the film-forming component of the clearcoat of a color-plus-clear composite coating. Examples include carbamate-aminoplast systems, polyurethanes, acid-epoxy systems and the like. However, many prior art systems suffer from application problems, compatibility problems with the pigmented basecoat, solubility problems and the like.
As a result, it would be advantageous to provide waterborne coating compositions having improved solids or % nonvolatile, popping resistance, flexibility, scratch & mar resistance, cold crack resistance, chip resistance and/or the like. At the same time, such improvements must be achieved without any decrease in environmental etch resistance or other commercially required performance property. It would be particularly advantageous to provide improved etch resistant waterborne coating compositions which have an increased % NV (nonvolatile) or decreased VOC (volatile organic content) at a sprayable viscosity.
It would be particularly desirable to provide aqueous coating compositions that are suitable for use as the clearcoat layer in color-plus-clear composite coatings and possess improved pop or popping resistance. “Pop resistance” or “popping resistance” as used herein refers to the resistance of an applied coating to form bubbles or pops at the surface of the film before or during the curing of the applied film. Such pop resistance is particularly important in clearcoats due to their higher film build requirements. Popping defects generally increase with increasing film build.
Accordingly, it is an object of the instant invention to provide curable waterborne coating compositions which provide all of the advantages of prior art coating compositions, especially good environmental etch resistance, but further exhibit improvement in one or more of the following performance parameters, i.e., popping resistance, flexibility, scratch and mar resistance, weathering resistance, UV durability, and/or chip resistance.
It is another object of the invention to provide a technology for improving one or more of the following performance parameters, i.e., % nonvolatile solids, popping resistance, flexibility, scratch and mar resistance, and/or chip resistance, in a wide variety of curable waterborne coating compositions and applications, such as primers, basecoats, clearcoats, two-component systems, anti-chip coating compositions, coatings for flexible substrates, and the like.
Most particularly, it is an object of the invention to provide a curable waterborne coating composition that is suitable for use as an automotive clearcoat and possesses improved pop resistance.